1. Field of the Invention
The present invention relates to a camera apparatus for recording a photographed still picture to a record medium and a recording method thereof.
2. Description of the Related Art
Digital cameras that record digital picture information to record mediums such as a floppy disk and a semiconductor memory are becoming common. A digital camera converts a photographed picture into a digital picture signal, compresses the digital picture signal, and records the compressed picture information to a record medium. A digital camera can also record a moving picture as well as a still picture.
JPEG (Joint Photographic Experts Group) format that is a format for compressing a still picture and MPEG (Moving Picture Experts Group) format are general-purpose encoding formats adopted by ISO. These formats are suitable for picture data photographed by a digital camera and used in a personal computer. In the JPEG format, a color still picture is compression-encoded by DCT (Discrete Cosine Transform) method. Coefficient data is quantized. The quantized output is encoded with variable length code. In contrast, in the MPEG format, a color moving picture is compression-encoded. In other words, a frame difference between an input picture and a motion-compensated predictive picture is compression-encoded by DCT method. When a digital camera can record a still picture and an audio signal corresponding thereto, a memo of a still picture can be recorded as an audio signal. However, since the JPEG format is designed to record and transmit information of still pictures, audio information corresponding to still pictures cannot be simultaneously recorded and transmitted. Likewise, in other still picture formats (GIF, TIFF, BMP, and so forth), a still picture and audio information corresponding thereto cannot be simultaneously recorded and transmitted. Although software that allows a still picture and audio information corresponding thereto to be simultaneously recorded and transmitted is known (for example, Exif V.20), it is not common. Even if audio attached still picture data is created in the format of such software, software for a player that reproduces the audio attached still picture data is not easily available.
In the MPEG format, there are three types of pictures that are an I picture (Intra-coded picture), a P picture (Predictive-coded picture), and a B picture (Bidirectionally predictive-coded picture).
In the MPEG format, when a P picture or a B picture is processed, since these pictures use an inter-frame motion compensation predictive process, the circuit scale of an encoder/decoder becomes large and the number of a software process steps remarkably increases. Thus, such a process is not suitable for a small, light, and inexpensive recording/reproducing apparatus such as a digital camera. To solve such a problem, it is necessary to generate an MPEG stream composed of only I pictures. However, MPEG1 (ISO -1172-2) standard defines that the minimum frame rated is 25 Hz for PAL or 29.97 Hz for NTSC. Thus, it is difficult to form a stream composed of only I pictures without P pictures or B pictures due to the restriction of the frame rate.
Therefore, an object of the present invention is to provide a camera apparatus and a recording method thereof corresponding to the MPEG format without increasing the circuit scale and the number of process steps.
Another object of the present invention is to provide a camera apparatus and a recording method thereof that encode a still picture and audio information corresponding thereto in MPEG format that is a general-purpose format.
Another object of the present invention is to provide a camera apparatus and a recording method thereof that allow the structure of an encoder/decoder that encode a moving picture signal in the MPEG format and a still picture signal in the JPEG format to be simplified.
Another object of the present invention is to provide a camera apparatus and a recording method thereof that simultaneously record a photographed still picture and audio information corresponding thereto.